What were to happen if I took one Unisom Natural Nights pill after it's expiration date?

I accidentally took one Unisom Natural Nights pill that I have had for awhile before reading the box. After rereading the information on the box I saw the expiration date. The date on the box was 01/2015 and it is currently 09/01/2015 so it has been expired for 8 months. Should I be concerned? Will anything bad happen? Will I have any weird side effects?